In recent years, optical brain-function imaging devices (light measuring devices) configured to perform measurements simply and noninvasively using light have been developed in order to observe brain activities. In such optical brain-function imaging devices, near-infrared light of three different wavelengths λ1, λ2 and λ3 (e.g. 780 nm, 805 nm and 830 nm) is irradiated by a light-transmitting probe arranged on a surface of a subject's head to the brain, and intensity (information on an amount of received light) A(λ1), A(λ2) and A(λ3) of the near-infrared light of the respective wavelengths λ1, λ2 and λ3 released from the brain are respectively detected by a light-receiving probe arranged on the surface of the head.
Then, from the information on the amount of light received A(λ1), A(λ2) and A(λ3) obtained in above manner, in order to obtain the product [oxyHb] of oxyhemoglobin concentration in cerebral blood flow and optical path length as well as the product [deoxyHb] of deoxyhemoglobin concentration and optical path length, simultaneous equations as shown in relational expressions (1), (2) and (3) are prepared using the Modified Beer Lambert Law, for example, and the simultaneous equations are solved (see Non-Patent Literature 1, for example). Furthermore, the total product ([oxyHb]+[deoxyHb]) of hemoglobin concentration and optical path length is calculated from the product [oxyHb] of the oxyhemoglobin concentration and the optical path length as well as the product [deoxyHb] of the deoxyhemoglobin concentration and the optical path length.A(λ1)=EO(λ1)×[oxyHb]+Ed(λ1)×[deoxyHb]  (1)A(λ2)=EO(λ2)×[oxyHb]+Ed(λ2)×[deoxyHb]  (2)A(λ3)=EO(λ3)×[oxyHb]+Ed(λ3)×[deoxyHb]  (3)
Furthermore, EO(λm) is a light absorbance coefficient of oxyhemoglobin for light of a wavelength λm, and Ed(λm) is a light absorbance coefficient of deoxyhemoglobin for light of the wavelength λm.
Here, a relationship between a portion to be measured and a distance (channel) between the light-transmitting probe and the light-receiving probe is described. FIG. 7(a) is a cross-sectional diagram showing the relationship between the portion to be measured and one pair of light-transmitting probe and light-receiving probe, and FIG. 7(b) is a plan diagram of FIG. 7(a).
A light-transmitting probe 12 is pressed against a light-transmitting point T on the surface of the subject's head, and a light-receiving probe 13 is pressed against a light-receiving point R on the surface of the subject's head. Then, light is irradiated from the light-transmitting probe 12, and light released from the surface of the head enters the light-receiving probe 13. Currently, of the light that has been irradiated from the light-transmitting point T on the surface of the head, the light that has passed through a banana-shaped area (area to be measured) reaches the light-receiving point R on the surface of the head. Accordingly, the information on the amount of light received A(λ1), A(λ2) and A(λ3) related to a portion to be measured S of the subject at a depth L/2, which is half of the distance along the line connecting the light-transmitting point T and the light receiving-point R along the surface of the subject's head from the middle point M of the line L connecting the light-transmitting point T and the light-receiving point R along the surface of the subject's head, is particularly obtained from among the area to be measured.
In addition, in the optical brain-function imaging devices, a near-infrared spectrometer, for example, is used in order to measure respectively the product [oxyHb] of the oxyhemoglobin concentration and optical path length, the product [deoxyHb] of the deoxyhemoglobin concentration and optical path length, and the product ([oxyHb]+[deoxyHb]) of the total hemoglobin concentration and optical path length related to a plurality of portions to be measured in the brain (see Patent Document 1, for example).
FIG. 8 is a block diagram showing one example of a schematic structure of a conventional near-infrared spectrometer. Furthermore, for convenience of viewing, multiple light-transmitting optical fibers and multiple light-receiving optical fibers are omitted.
A near-infrared spectrometer 201 has a housing 11 in rectangular parallelepiped form.
Inside the housing 11, a light source 2 configured to emit light, a light source driving mechanism 4 configured to drive the light source 2, a light detector 3 configured to detect light, an A/D (A/D converter) 5, a light transmission and reception control unit 21, an analysis control unit 22, and a memory 23 are included. In addition, on the outside of the housing 11, sixty-four light-transmitting probes 12, sixty-four light-receiving probes 13, sixty-four light-transmitting optical fibers 14, sixty-four light-receiving optical fibers 15, a display device 26 having a monitor screen 26a or the like, and a keyboard (input device) 27 are included.
The light source driving mechanism 4 drives the light source 2 by a driving signal inputted from the light transmission and reception control unit 21. The light source 2 is, for example, semiconductor lasers LD1, LD2 and LD3 capable of emitting the near-infrared light with three different wavelengths λ1, λ2 and λ3.
The light detector 3 is a detector configured to detect the near-infrared light respectively and thus outputs light reception signals (information on the amount of light received) A(λ1), A(λ2) and A(λ3) to the light transmission and reception control unit 21 via the A/D 5, and is, for example, a photomultiplier or the like.
The light-transmitting optical fiber 14 and the light-receiving optical fiber 15 are in tubular form having a diameter of 2 mm and a length of 2 m˜10 m, and are capable of transmitting the near-infrared light along an axial direction so that the near-infrared light entering from one end passes through the inside and exits from another end and that the near-infrared light entering from the another end passes through the inside and exits from the one end.
One light-transmitting optical fiber 14 is connected to one light-transmitting probe 12 and one semiconductor laser LD1, LD2 and LD3 of the light source 2 at two ends so that the two are away from each other at a set length (2 m˜10 m).
One light-receiving optical fiber 15 is connected to one light-receiving probe 13 and one photomultiplier of the light detector 3 at two ends so that the two are away from each other at a set length (2 m˜10 m).
In such near-infrared spectrometer 201, in order to cause the sixty-four light-transmitting probes 12 and the sixty-four light-receiving probes 13 to contact the surface of the subject's head in a predetermined arrangement, a holder 30 is used. FIG. 9 is a plan diagram showing one example of the holder 30 into which sixty-four light-transmitting probes and sixty-four light-receiving probes are inserted.
The light-transmitting probes 12T1˜12T64 and the light-receiving probes 13R1˜13R64 are alternately arranged with sixteen in the vertical direction and sixteen in the horizontal direction. Accordingly, probe intervals between the light-transmitting probes 12 and the light-receiving probes 13 become constant, and the information on the amount of light received A(λ1), A(λ2) and A(λ3) at a specific depth from the surface of the head is obtained. Furthermore, a channel of 30 mm is generally used, and in the case where the channel is 30 mm, it is considered that the information on the amount of light received A(λ1), A(λ2) and A(λ3) at depths of 15 mm˜20 mm from the middle point of the channel may be obtained. That is, a position at depths of 15 mm˜20 mm from the surface of the head approximately corresponds to portions on the surface of the brain, and thus, the information on the amount of light received A(λ1), A(λ2) and A(λ3) concerning the brain's activities is obtained.
By the way, in such positional relationship between the sixty-four light-transmitting probes 12T1˜12T64 and the sixty-four light-receiving probes 13R1˜13R64) is necessary to adjust the timing of irradiating light from the light-transmitting probes 12 and the timing of receiving light by the light-receiving probes 13, so that one light-receiving probe 13 only receives the light irradiated from one light-receiving probe 13, but does not receive the light irradiated from a plurality of light-transmitting probes 12. For this reason, in the memory 23, a control table showing the timing of emitting light by the light source 2 and the timing of detecting light by the light detector 3 is stored.
The light transmission and reception control unit 21, in which such control table is stored in the memory 23, outputs a driving signal configured to transmit light to one light-transmitting probe 12 to the light source driving mechanism 4 at a predetermined time and detects the light reception signals (information on the amount of light received) received by the light-receiving probes 13 using the light detector 3.
As a result, when viewed in a plan view as shown in FIG. 9, collection of a total of 232 pieces (S1˜S232) of information on the amount of light received A(λ1), A(λ2) and A(λ3) is carried out.
Then, based on the total of 232 pieces of information on the amount of light received A(λ1), A(λ2) and A(λ3), the analysis control unit 22 calculates the product [oxyHb] of oxyhemoglobin concentration and optical path length, the product [deoxyHb] of deoxyhemoglobin concentration and the optical path length, and the product ([oxyHb]+[deoxyHb]) of the total hemoglobin concentration and optical path length from intensity of passing light of respective wavelengths (absorption wavelength of oxyhemoglobin and absorption wavelength of deoxyhemoglobin) using the relational expressions (1), (2) and (3).
However, to mount the holder 30 as described above on the surface of the subject's head was very time-consuming for a doctor or the like, and was very stressful for the subject to be physically restrained for a long time. In addition, it was very hard for the subject to exercise such as rehabilitation every day.
Accordingly, the present applicants had previously conceived of a comb-shaped holder to push hair aside by the holder itself so as to enable the subject to exercise such as rehabilitation while mounting the holder on the subject's head in a short time, and had filed patent applications therefor (see Patent Document 2 and Patent Document 3, for example). FIG. 3 is a plan diagram showing one example of the comb-shaped holder. A holder 60 is provided with one linear trunk unit 62 and five linear branches 61 and 63. According to such holder 60, it is possible to mount the holder 60 on the head in a short time.
Meanwhile, a brain wave measurement method has also been known to perform measurements simply and noninvasively inside a living body by using a fact that an electric potential of the surface of the subject's head corresponds to accumulation and summation of electrical activities of nerve cells and synapses. Accordingly, an electroencephalograph (EEG) provided with a holder having a plurality of EEG electrodes and one reference electrode has been developed. In the EEG, potential difference (potential information) is detected by the EEG electrodes arranged on the surface of the subject's head and by the reference electrode arranged in the subject's ears or the like.
Accordingly, the present applicants had previously conceived of a netlike holder capable of executing measurements by an optical bioinstrumentation device and by an EEG at the same time, and filed patent applications therefor (see Patent Document 4, for example).